Head First Java a brain-Friendly Guide Kathy Sierra and Bert Bates

c
to variable 
d
. But what does this mean? It’s like saying, “Take the bits in 
c
, make a copy of them, and stick that
copy into 
d
.”
Both c and d refer to the same object.
The c and d variables hold two different copies of the same value. Two remotes programmed to one TV.
References: 3
Objects: 2
c = b;
Assign the value of variable 
b
to variable 
c
. By now you know what this means. The bits inside variable 
b
are
copied, and that new copy is stuffed into variable 
c
.
Both b and c refer to the same object.
References: 3
Objects: 2

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Life and death on the heap
Book b = new Book();
Book c = new Book();
Declare two Book reference variables. Create two new Book objects. Assign the Book objects to the reference
variables.
The two book objects are now living on the heap.
Active References: 2
Reachable Objects: 2
b = c;
Assign the value of variable 
c
to variable 
b
. The bits inside variable 
c
are copied, and that new copy is stuffed into
variable 
b
. Both variables hold identical values.
Both b and c refer to the same object. Object 1 is abandoned and eligible for Garbage Collection (GC).
Active References: 2

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Reachable Objects: 1
Abandoned Objects: 1
The first object that 
b
referenced, Object 1, has no more references. It’s 
unreachable
.